Topography and numerical densities of intramembrane particles in chemical carcinogen-induced urinary bladder carcinomas in Fischer rats.

Integral membrane proteins are visualized as intramembrane particles (IMP) at the cleaved surfaces of freeze-fractured plasma membranes. Topographical distributions of the IMP of the urinary bladder epithelial cells membranes in normal Fischer rat bladder and noninvasive and invasive N-(4-(5-nitro-2-furyl)-2-thiazolyl)formamide (FANFT)-induced bladder tumors are shown to be significantly different. Using several statistical methods that test IMP topography vis-a-vis the Poisson (random) hypothesis, it is demonstrated that IMP are mathematically randomly distributed in the large majority of plasma membranes of cells in normal rat bladder epithelium and in invasive N-(4-(5-nitro-2-furyl)-2-thiazolyl)formamide tumors. In noninvasive rat bladder carcinomas, IMP are in a lattice-like arrangement in half of the tumor cells and randomly distributed in the remainder. IMP numerical densities are also altered in the course of neoplastic transformation. IMP are equally increased above control values in both noninvasive and invasive N-(4-(5-nitro-2-furyl)-2-thiazolyl)formamide tumors. Although transformation into noninvasive tumors is associated with increased numbers of IMP, there is no evidence that this parameter is specifically related to tumor biologic behavior in this model system.